1. Field of the Invention
The present invention relates to a water-base ink composition comprising a colorant component, selected from dyes or pigments, an alcohol, a surfactant and/or a penetrating organic solvent, a humectant, a resin emulsion, and water.
2. Background Art
Ink jet recording is a printing method wherein droplets of ink are ejected and deposited on recording media, such as paper, to perform printing. The feature of the ink jet recording method is that images having a combination of high resolution with high quality can be printed at a high speed by means of a relatively inexpensive apparatus.
Ink compositions used in ink jet recording generally comprise water as a main ingredient and, added to water, a colorant component and a humectant, such as glycerin, for clogging preventive purposes and the like. A large number of water soluble dyes have been used as the colorant component for the ink composition for ink jet recording, for example, from the viewpoints of high chroma of the coloring material, a wide variety of usable coloring materials, and solubility in water.
On the other hand, in recent years, the use of pigments as a colorant component in water-base inks for ink jet recording has been studied from the viewpoint of realizing an improvement in weatherfastness properties, such as lightfasthness, gasfastness, and waterfastness, of records that cannot be attained by water soluble dyes without difficulties.
In order to yield sharp images, simultaneously satisfying requirements, for example, for printing properties such as a high level of color development and a low level of bleeding, a high level of penetrating properties which can cope with high-speed printing, and ejection stability properties free from droplet trajectory directionality problems of ink ejected from head nozzles is required of water-base inks for ink jet recording.
However, it should be noted that an increase in penetrating properties of ink to a very high level is disadvantageous in that, since the ink penetrates into a recording medium, the ink is less likely to stay on the surface of the recording medium, leading to a deterioration in homogeneity of filled images. Further, some combination with a water soluble organic solvent or a surfactant used results in unstable ink ejection.
To overcome these problems, Japanese Patent Laid-Open Nos. 239068/1992 and 322307/1994 propose the use of an acetylene glycol surfactant to regulate the penetrability of ink into recording media. Further, Japanese Patent Laid-Open Nos. 3100/2003 and 192969/2003 propose the addition of a monovalent or divalent branched alcohol with a specific chain length from the viewpoint of improving the penetrability of ink into recording media. Furthermore, for example, Japanese Patent Laid-Open No. 96345/2003 discloses an ink composition with a predetermined viscosity comprising a specific divalent alcohol and a penetrating agent.
In water-base ink compositions for use in ink jet recording, in addition to the colorant component, various additives, particularly water soluble organic solvents, are added from the viewpoint of optimizing various properties required of inks. Regarding the water soluble organic solvent, for example, humectants for preventing ink from drying, penetrating organic solvents or, surfactants for suppressing ink penetration, and organic amines for pH adjustment are added to ink.
When monovalent or divalent branched alcohols with a specific chain length are used, however, some combination thereof with other organic solvents or surfactants has sometimes resulted in unstable ink ejection. Further, there is a demand for improved color development on plain paper.